Incandescent lamp and method of manufacture



Oct. 3, 1944. I L.-W. CURTIS 2,359,302

INCANDESCENT LAMP AND METHOD OF MANUFACTURE Filed June 11, 1942 INVENTOR[am/v W CuRT/s BY am 1 M Y 7 ATTORNEYS Patented Oct. 3, 1944INCANDESCENT LAMP AND METHOD OF MANUFACTURE Lorin w. own, Verona, N. 1.,alslnor to rung- Sol Lamp Works Inc., Newark, N. J., a corporae tion ofDelaware Application June 11, 1942, Serial No. 44s,ss4

6 Claims. (01. 115-40) This invention relates to incandescent lamps andparticularly lamps of the miniature type.

The invention relates to the mounting and the welding of the legs of thecoiled filaments of miniature incandescent lamps to the filament supportwires and more particularly to the provision of reinforced weldstherefor. One object of the invention is a novel and improved method offorming coiled'filaments for miniature incandescent lamps withreinforced legs for facilitating the mounting of the filaments upon thewire supports.

Further objects of the invention will hereinafter appear.

For a better understanding of the invention reference may be had to theaccompanying drawmount of the incandescent lamp embodying the invention,the glass envelope or bulb and the base being omitted for convenience inillustration. This mountincludes a'glass press I and a pair of filamentsupport wires 2 having'mounted thereon a coiled-coil filament 3, thelatter being formed of a continuous coil of fine filamentary wire suchas tungsten coiled'about itself into larger Lcoils with legs 4 welded atthe points 5 to the support wires 2. The legs 4 comprise cores 6 withinthe primarycoil for reinforcing them for the welding formed at thepoints 5. By providing the legs 4 with the reinforcing cores 6 the legs4 of the filament may be firmly and permanently welded to the mountwires 2 with facility.

The coiled-coil filament 3 is formed and prepared for the mountingoperation by first forming the filament with the primary mandrel thereinand then dissolving out the intermediate portion of the primary mandrelto leave the leg filament portions of the mandrel in the coil as areinforcement for mounting and welding the filament. By thus providingfor the utilization of portions of the primary mandrel about which thewire is closely wound as a reinforcing means for the mount and weld, themount meets the require ments as to endurance and ruggedness of construction for heavy duty service, such for example as used on tanks andthe like. This method alse eliminates the conventional and tedious stepin the preparation of the filament for the mount of making inserts ofsmaller diameter into the filament legs which was usually accompaniedwith theproblem of retaining the more or less loosely mounted inserts inproper place during the welding operation.

Th method of forming and preparing the coiled-coil filament for mountingis illustrated in Figs". 1 to 5, inclusive. Fig. 1 illustrates theforming of the coiled filament about the primary mandrel 6', thismandrel being of any suitable metal, as for example brass, iron ormolybdenum, and Fig. 2 illustrates the filament after the coiling of thefilament into the larger coil with the primary mandrel 6 therein. Afterthe filament is thus formed, the filament legs 4 are then coated withsome substance which is neutral to the acid conventionally used fordissolving the mandrel i cut of the coil. I have found suitable for thispurpose a high melting temperature wax contained in a conventionallyillustrated container 1 into which the legs 4 of the filament are dippedby hand or otherwise. I have obtained good results with the use ofcarnauba wax, but any wax with a high melting point could be utilized,that is a melting point above the temperature of the acid bath. It ismelted and maintained in a liquid state in a shallow dish or container 1which is heated in any suitable manner, as for example by a hot plate,omitted from the drawing for convenience in illustration. The filamentlegs 4 thus dipped in the coating wax or other coating material 8 isillustrated in Fig. 4, which illustrates a coating of material 8 onthese legs. With the filament legs thus coated, as shown in Fig. 4, the

filament is immersed in an acid bath for the purpose of dissolving outthe mandrel 6' from the coiled-coil part of the filament so as to leaveonly the cores 6 in the end or leg portions. Fig. 4 shows the filamentafter the dissolution of mandrel 6' has taken place. The acid bath usedfor this purpose depends upon the character of the mandrel. With amandrel of brass a conventional bath is one of nitric acid. With" amandrel of iron,

a bath of hydrochloric acid is conventional and for molybdenum a bath ofnitric and sulphuric acids mixed may be employed. In dissolving themandrel, it is essential to keep the solution cooled below the incitingpoint of the wax, since there is a considerable amount of heat generatedfrom the reaction of the mandrel with the acid. This may-bejd'one in abath of cold water. If too many coils are placed in the acid at onetime, there may be a sumcient amount of heat arising from the reactionto melt oil the wax coating 8 of Fig. 4 and allow the acid to attack themandrel part or cores 6 within the leg sections and, accordingly,

filament in an acid 'mary mandrel portion intermediate the legs and arelatively small quantity of filaments are treated at one time whendissolving the primary mandrel 6 out of the filament. With thecoiledcoil filament thus obtained, as shown in Fig. 4, the next step isthe removal of the wax or neutral coating 8 from the legs 4 of thefilament. Th1! may be eflected with a hot caustic or with a suitable waxsolvent; as ior example ethylen di- Fig. 5 and in this form it is nowready to situated by welding the iegs 4 to t e mount, sum port wires 2with me c res 5 in the legs which formed part of the original primarymandrel chloride. The filament fOlllld is shown army and snugly held andreta ned time eieseiy wound coils of the legs or ma icure g Thefilament, mai be subieet to e ventio nai treatiiiiitswitli a causticoath and rinsing in flat ath to disso v out the iS-ri':

to leave the coated leg mandrel portions as reiniorcing cores for thelegs, removing the neutral coatings from the legs, and then welding themandrel supported legs of the filament to filament support wires.

2. The method of forming and mounting I coiled-coil filament in anincandescent lamp which consists in forming a coiled-coil filament withstraight leg or end portions havihg a primary mandrel extendingthroughout the smaller filament coil, coating the leg portions of thefilament with a neutral substance which melts at I high temperature,immersing the filament in an acid bath to dissolve out the primarymandrel portion intermediate the legs and to leave the coated legmandrel portions as reinforcing cores for the legs, dissolving theneutral coatings from the legs, and then welding the mandrel supportedlegs of the filament to filament support wires.

3. The method forming and mounting a coiled-coil filament inanincandescent lamp which consists in forming 'a coiled-coil filament withstraight leg or end portions having a pri- Fill mar mandrel extendingthroughout the smaller aasasoa filament coil, coatinfl the leg portionsof the filament with wax, immersing the filaments in an acid bath todissolve out the primary mandrel portion intermediate the legs and toleave the coated leg mandrel portions as reiniorcing'cores lot the legs,dissolving the wax coatings from the legs; and then welding the mandresupported legs or the filament to lament support wires.

1. The method of tanning and mounting a coiled-coil e ement in anincandescen imp tiniest cdiisistfi iii taming a eaued -eau filament withstraight leg or eiiujxsr'uans having a priiiiary mandrel extending throighojit the filament, coating the leg portions of the filament with aneutral substan e, the elements in' a acid bath to dissolve out theprimary man rel screenwriter-mediate the legs sea to leave the ea dill3mta' s i ipr inz ti t th legs, maintaining tlie'acid bath at atemperature during the di i ti n ma b gw he tan e, removingthe hiitralnits nan the malaria sii f lidited legs a: the filament t5 filamentwires. 1 I I 'I e 'ifit i 6 aml 6 ime tureinsans c nt ambsa iith ips lv. oi 1017mm" a coiled ,illafiient witli ls'traight e; o an t on e? 1 1i-l i l m n ala throughout'the filam t and oifja difi'erent in t'al o t aof w h th m l emsn i term ai in: the leg portiog oftige iiiar'rient ,anet tral intimate i8 ilrzit'ttmg nit Elmira 38? tie against acid attack,wholly immersing the filament in an acid bath to dissolve out themandrel portion intermediate the legs and to leave the coated legportions of the mandrel as reinforcing cores for the legs and removingthe neutral coat.- ings from the legs preparatory to mounting thefilament thus formed by fastening the reinforced straight leg portionsto filament supportwirea.

0. The method 01 iorming and mounting a toiled-coil filament in anincandescent lamp which consists in forming a coiled-coil filament withstraight smaller coil portions having a primm mandrel'ex'tendin'gthroughout the smaller coil, coating the straight portions of thecoiledcoil filament with a neutral substance, immersing the filament inan acid bath to dissolve out the mandrel portion intermediate thestraight por-' tions and to leave the coated straight mandrel portionsas reinforcing cores therefor, removing the neutral coating from thestraight portions, and then fastening the mandrel supported straightportions oi the coiled-coil filament to filament support wires.

LORIN W.- CURTIS.

